Controller for internal combustion engine

ABSTRACT

To provide a controller that can slow down progression of deterioration of an internal combustion engine caused by repeated occurrence of LSPI. An index value of the degree of deterioration of the internal combustion engine caused by LSPI is calculated. If the index value exceeds a first threshold, when the temperature of cooling water that cools a part of the peripheral wall of a cylinder that is close to a combustion chamber is lower than a threshold temperature, and the internal combustion engine is running in a determined operational region set in a low speed and high load region, the proportion of fuel injection by an in-cylinder injection valve is reduced to increase the proportion of fuel injection by a port injection valve compared with before the index value exceeds the first threshold, thereby suppressing occurrence of LSPI.

FIELD

The present disclosure relates to a controller for an internal combustion engine, in particular, to a controller for an internal combustion engine provided with an in-cylinder injection valve and a port injection valve. More specifically, it relates to a controller suitable for use with an internal combustion engine a part of which has a great influence on the temperature of the intake air is cooled by cooling water at a temperature lower than cooling water that cools a peripheral wall of a cylinder.

BACKGROUND

There is a known abnormal combustion called low speed pre-ignition (LSPI). LSPI is an abnormal combustion before the ignition timing that is caused by ignition of an oil drop dispersed from the wall of the cylinder into the combustion chamber, a deposit peeling off the wall of the cylinder during combustion, or a deposit peeling off the intake port and entering the combustion chamber. LSPI is particularly likely to occur in a low speed and high load region. LSPI is also an abnormal combustion that is likely to occur in an internal combustion engine that involves in-cylinder injection. Fuel injected from the in-cylinder injection valve tends to be mixed with oil on the wall of the cylinder before evaporating, and thus the oil is diluted with the fuel. As the oil is diluted with the fuel, the surface tension of the oil film covering the wall of the cylinder decreases, and the oil is more likely to be dispersed into the combustion chamber. This holds true not only for an internal combustion engine provided with only an in-cylinder injection valve but also for an internal combustion engine provided with an in-cylinder injection valve and a port injection valve. This is because, with normal settings, the proportion of fuel injection by the in-cylinder injection valve is set to be high (typically, 100%) in a low speed and high load region.

LSPI causes torque fluctuations and thus deterioration of the operability of the internal combustion engine. In addition, as LSPI repeatedly occurs, the main body (specifically, such as a cylinder block or a cylinder head) and parts (specifically, such as a piston ring, a piston or a valve) of the internal combustion engine are deteriorated.

JP 2014-240627 discloses a solution to the former problem. According to the solution, when occurrence of LSPI is detected, the proportion of the fuel injection by the in-cylinder injection valve is lowered to raise the proportion of the fuel injection by the port injection valve, thereby suppressing occurrence of LSPI. JP 2013-204507 discloses a solution to the latter problem. According to the solution, when the number of times of occurrence of LSPI exceeds a threshold set in accordance with the mileage, the air-fuel ratio is changed to the rich side, thereby suppressing occurrence of LSPI.

However, the ratio of fuel injection between the in-cylinder injection valve and the port injection valve and the air-fuel ratio are adapted to achieve optimal fuel consumption and emission performance. Therefore, it is undesirable to change those ratios from the viewpoint of fuel consumption and emission performance. The techniques disclosed in JJP 2014-240627 and JP 2013-204507 can attain the object of suppressing occurrence of LSPI but can cause side effects, such as deterioration of fuel consumption and emission performance. Furthermore, according to the technique disclosed in JP 2013-204507, changing the air-fuel ratio to the rich side may facilitate dilution of the oil on the wall of the cylinder with fuel, which can lead to occurrence of LSPI.

The inventors of the patent application are conducting a study regarding providing a cylinder block of an internal combustion engine with two cooling water flow channels. More specifically, the inventors are conducting a study regarding providing a first cooling water flow channel used for cooling the whole of the peripheral wall of the cylinder and a second cooling water flow channel used for locally cooling parts that have a great influence on the temperature of the intake air, and setting the temperature of the cooling water flowing in the second cooling water flow channel to be lower than the temperature of the cooling water flowing in the first cooling water flow channel. Specifically, the parts that have a great influence on the temperature of the intake air are the intake port and a part of the peripheral wall of the cylinder that is close to the combustion chamber.

With this configuration, the parts that have a great influence on the temperature of the intake are can be intensively cooled. Therefore, occurrence of an abnormal combustion (including not only LSPI but also knocking) can be effectively suppressed without increasing friction, and the charging efficiency of the intake air can also probably be improved. In addition, the ratio of fuel injection and the air-fuel ratio do not have to be changed later, the intended fuel consumption and emission performance can probably be maintained while suppressing occurrence of an abnormal combustion.

The technique under study described above (which is not known at the time of application of this patent) still has a problem. If the temperature of the cooling water flowing in the second cooling water flow channel excessively decreases for some reason, evaporation of the fuel injected from the in-cylinder injection valve is further slowed down, and therefore, the oil on the wall of the cylinder is further diluted with the fuel. As the oil is further diluted with the fuel, the oil is more likely to be dispersed into the combustion chamber as described above, and deposits on the wall of the cylinder markedly increase. If the second cooling water flow channel is used to cool the intake port, the intake port is excessively cooled to facilitate growth of deposits, and the deposits may peel off and enter the combustion chamber. Once dispersed into the combustion chamber, oil drops and deposits can cause occurrence of LSPI. Therefore, as the oil drops and deposits increase, the possibility of occurrence of LSPI increases. That is, the technique under study described above still needs a measure against LSPI.

Among other problems concerning LSPI, a serious problem is that the internal combustion engine is deteriorated as LSPI repeatedly occurs. If each occurrence of LSPI is suppressed by controlling the internal combustion engine, the fuel consumption and emission performance are deteriorated as a side effect, although the operability is improved. These days, the fuel consumption and emission performance tend to take precedence over the operability. However, if each occurrence of LSPI is ignored from the viewpoint of the fuel consumption and emission performance, the internal combustion engine is deteriorated as LSPI repeatedly occurs, the useful life of the internal combustion engine is shortened and the mileage of the vehicle is significantly reduced. Thus, some measures have to be taken to suppress LSPI.

The present disclosure has been devised in view of the problems described above, and an object of the present disclosure is to provide a controller for an internal combustion engine that can slow down progression of deterioration of the internal combustion engine due to repeated occurrence of LSPI while reducing deterioration of fuel consumption and emission performance.

SUMMARY

A controller for an internal combustion engine according to the present disclosure is used with an internal combustion engine that comprises an in-cylinder injection valve that directly injects fuel into a combustion chamber formed in an upper part of a cylinder, and a port injection valve that injects the fuel into an intake port. The internal combustion engine further comprises a first cooling water flow channel used to cool a part of a peripheral wall of the cylinder with first cooling water, and a second cooling water flow channel used to cool a part that has a great influence on the temperature of the intake air with second cooling water at a lower temperature than the first cooling water. The part cooled by the second cooling water flow channel includes at least one of the intake port and a part of the peripheral wall of the cylinder that is closer to the combustion chamber than the part cooled by the first cooling water flow channel.

The controller for an internal combustion engine according to the present disclosure is configured to calculate an index value of a degree of deterioration of the internal combustion engine caused by LSPI, and to perform a first process for suppressing occurrence of LSPI based on the index value as a determination criterion. More specifically, controller is configured to, if the index value exceeds a first threshold, the perform the first process for suppressing occurrence of LSPI on a condition that the temperature of the second cooling water is lower than a threshold temperature, and the internal combustion engine is running in a determined operational region set in a low speed and high load region. In the first process, the proportion of fuel injection by the in-cylinder injection valve is reduced to increase the proportion of fuel injection by the port injection valve compared with before the index value exceeds the first threshold.

With the controller configured as described above, the first process for suppressing occurrence of LSPI is not simply performed when the index value exceeds the first threshold but performed only when a condition under which LSPI is highly likely to occur is satisfied, that is, only when the temperature of the second cooling water is lower than the threshold temperature, and the internal combustion engine is running in the determined operational region. As a result, side effects of suppression of occurrence of LSPI, such as deterioration of fuel consumption and emission performance, can be suppressed. Furthermore, in the first process, since the proportion of fuel injection by the in-cylinder injection valve is reduced to increase the proportion of fuel injection by the port injection valve, dilution of oil on the wall of the cylinder with the fuel, which can lead to occurrence of LSPI, can be slowed down. As a result, the frequency of occurrence of LSPI can be reduced to slow down progression of deterioration of the internal combustion engine.

In a preferred embodiment of the present disclosure, the controller is further configured to perform a second process for suppressing occurrence of LSPI based on the index value described above as a determination criterion. More specifically, the controller is configured to, if the index value exceeds a second threshold that is greater than the first threshold, perform the second process for suppressing occurrence of LSPI on a condition that the internal combustion engine is running in the determined operational region. In the second process for suppressing occurrence of LSPI, the temperature of the second cooling water is increased compared with before the index value exceeds the second threshold.

With such a configuration, if the first process is not enough to reduce to the frequency of occurrence of LSPI, and the index value exceeds the second threshold that is greater than the first threshold, the second process for suppression occurrence of LSPI is performed in addition to the first process. In the second process, since the temperature of the second cooling water is increased, the temperature of the wall of the cylinder (the part of the cylinder closer to the combustion chamber) increases. Therefore, dilution of the oil on the wall of the cylinder with the fuel, which can lead to occurrence of LSPI, can be effectively suppressed, so that the frequency of occurrence of LSPI can be reduced, and progression of the deterioration of the internal combustion engine can be slowed down. However, increasing the temperature of the wall of the cylinder has a disadvantage that the charging efficiency decreases or knocking is more likely to occur. The disadvantage is minimized by performing the second process only when the internal combustion engine is running in the determined operational region rather than simply performing the second process when the index value exceeds the second threshold.

As described above, the controller for an internal combustion engine according to the present disclosure can slow down progression of deterioration of the internal combustion engine caused by repeated occurrence of LSPI while suppressing deterioration of fuel consumption and emission performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a configuration of an internal combustion engine according to an embodiment;

FIG. 2 is a diagram showing a configuration of a cooling system for the internal combustion engine according to the embodiment;

FIG. 3 is a flowchart showing a flow of an LT flow rate control;

FIG. 4 is a diagram showing an LSPI occurrence region;

FIG. 5 is a flowchart showing a flow of a first LSPI suppression control;

FIG. 6 is a graph for illustrating an effect of the first LSPI suppression control;

FIG. 7 is a flowchart showing a flow of a second LSPI suppression control; and

FIG. 8 is a graph for illustrating an effect of the second LSPI suppression control.

DESCRIPTION OF EMBODIMENTS

In the following, an embodiment of the present invention will be described with reference to the drawings. Any mention of a numerical value such as the number, quantity, amount or range of an entity in the embodiment described below is not intended to limit the present disclosure to the numerical value unless otherwise specified or unless it is obvious that the numerical value is intended to be limiting. In addition, any structure, step or the like described in the embodiment is not essential for the present disclosure unless otherwise specified or unless it is obvious that the structure, step or the like is essential.

1. Configuration of Internal Combustion Engine

FIG. 1 is a schematic diagram showing a configuration of an internal combustion engine according to this embodiment. FIG. 1 shows a projection of components of an internal combustion engine 1 on a plane perpendicular to a crank shaft. The internal combustion engine 1 according to this embodiment is a spark ignition multi-cylinder engine with a plurality of cylinders 4 (referred to simply as an engine, hereinafter). The number and arrangement of the cylinders 4 are not particularly limited. The engine 1 has a cylinder block 3 in which the cylinders 4 are formed and a cylinder head 2 provided on the cylinder block 3 with a gasket (not shown) interposed therebetween. A piston 8 is disposed in the cylinder 4 in such a manner as to reciprocate in the axial direction of the cylinder 4. An upper space in the cylinder 4 below the lower surface of the cylinder head 2 forms a combustion chamber 6 having a pent roof-like shape.

In the cylinder head 2, an intake port 10 and an exhaust port 12 that are in communication with the combustion chamber 6 are formed. The intake port 10 is provided with an intake valve 14 at an opening thereof to the combustion chamber 6, and the exhaust port 12 is provided with an exhaust valve 16 at an opening thereof to the combustion chamber 6. Although not shown, the intake port 10 branches into two parts at a midpoint between an inlet thereof formed in the outer surface of the cylinder head 2 and the opening thereof to the combustion chamber 6. Upstream of the branch point, the intake port 10 is provided with a port injection valve 24 that injects fuel into the intake port 10. An in-cylinder injection valve 26 that injects fuel into the combustion chamber 6 is provided under the intake port 10 between the two parts of the intake port 10, the tip end of the in-cylinder injection valve 26 facing to the combustion chamber 6. Furthermore, an ignition plug 20 and a combustion pressure sensor 22 that measures combustion pressure are provided in the vicinity of the apex of the combustion chamber 6.

The engine 1 is provided with an electronic control unit (ECU) 100. The ECU 100 has at least an input/output interface, a ROM, a RAM and a CPU. The input/output interface is provided to receive sensor signals from various sensors attached to the engine 1 or the vehicle and to output operation signals to actuators provided in the engine 1. The ROM stores various kinds of control data including various control programs or maps used for controlling the engine 1. The CPU reads control programs from the ROM, executes the programs, and generates operational signals based on the received sensor signals.

2. Configuration of Cooling System

FIG. 2 is a diagram showing a configuration of a cooling system for the engine 1. The cooling system for the engine 1 includes two cooling water circulation systems 30 and 50 for supplying cooling water. Cooling water is supplied to both the cylinder block 3 and the cylinder head 2 of the engine 1. Both the cooling water circulation systems 30 and 50 are independent closed loops through which cooling water at different temperatures can be circulated. In the following, the cooling water circulation system 30 through which cooling water at a relatively low temperature is circulated will be referred to as an “LT cooling water circulation system”, and the cooling water circulation system 50 through which cooling water at a relatively high temperature is circulated will be referred to as a “HT cooling water circulation system”. The cooling water circulated through the LT cooling water circulation system 30 will be referred to as “LT cooling water”, and the cooling water circulated through the HT cooling water circulation system 50 will be referred to as “HT cooling water”. “LT” is an abbreviation of low temperature, and “HT” is an abbreviation of high temperature.

The LT cooling water circulation system 30 includes an in-head LT cooling water flow channel 32 formed in the cylinder head 2 and an in-block LT cooling water flow channel 34 formed in the cylinder block 3. The in-head LT cooling water flow channel 32 is provided in the vicinity of the intake port 10 (see FIG. 1). The in-block LT cooling water flow channel 34 is provided to surround a peripheral wall part of the cylinder 4 (see FIG. 1) that is close to the combustion chamber 6 (see FIG. 1), that is, a part of the cylinder 4 that is likely to be exposed to the flow of intake air swirling in the combustion chamber 6. The temperature of the intake port 10 and the intake valve 14 (see FIG. 1) and the temperature of the wall surface of an upper part of the cylinder 4 are sensitive to knocking. If these components are intensively cooled with the in-head LT cooling water flow channel 32 and the in-block LT cooling water flow channel 34, occurrence of knocking in a high load region and occurrence of LPSI in a low speed and high load region can be effectively suppressed. The in-head LT cooling water flow channel 32 and the in-block LT cooling water flow channel 34 are connected to each other via openings formed in the interface between the cylinder head 2 and the cylinder block 3.

A cooling water inlet and a cooling water outlet that are in communication with the in-head LT cooling water flow channel 32 are formed in the cylinder head 2. The cooling water inlet in the cylinder head 2 is connected to a cooling water outlet of an LT radiator 40 by a cooling water inlet pipe 36, and the cooling water outlet in the cylinder head 2 is connected to a cooling water inlet of the LT radiator 40 by a cooling water discharge pipe 38. The cooling water inlet pipe 36 and the cooling water discharge pipe 38 are connected to each other by a bypass pipe 42 that bypasses the LT radiator 40. A three way valve 44 is provided at a branch point at which the bypass pipe 42 branches from the cooling water discharge pipe 38. An electric water pump 46 that causes circulation of the LT cooling water is provided on the cooling water inlet pipe 36 at a point downstream of a merging point at which the bypass pipe 42 merges with the cooling water inlet pipe 36. The discharge volume of the electric water pump 46 can be changed as desired by adjusting the power of a motor thereof. A temperature sensor 48 that measures the temperature of the LT cooling water having passed through the engine 1 (referred to as an LT water temperature, hereinafter) is attached to the cooling water discharge pipe 38 at a point upstream of the three way valve 44. In this embodiment, the LT water temperature means the outlet cooling water temperature measured by the temperature sensor 48.

The HT cooling water circulation system 50 includes an in-block HT cooling water flow channel 54 formed in the cylinder block 3 and an in-head HT cooling water flow channel 55 formed in the cylinder head 2. The in-block HT cooling water flow channel 54 forms a main part of a water jacket that surrounds the peripheral wall of the cylinder 4 and cools the whole of the peripheral wall of the cylinder 4, whereas the in-block LT cooling water flow channel 34 described above is locally provided. The in-head HT cooling water flow channel 55 is provided to extend from the vicinity of an exhaust port to the vicinity of the intake ports. The intake air flowing through the intake port 10 is first cooled by the HT cooling water flowing through the in-head HT cooling water flow channel 55 and then cooled by the LT cooling water, which is at a lower temperature than the HT cooling water, flowing through the in-head LT cooling water flow channel 32. The in-head HT cooling water flow channel 55 and the in-block HT cooling water flow channel 54 are connected to each other via openings formed in the interface between the cylinder head 2 and the cylinder block 3.

In the cylinder block 3, a cooling water inlet and a cooling water outlet that are in communication with the in-block HT cooling water flow channel 54 are formed. The cooling water inlet in the cylinder block 3 is connected to a cooling water outlet of an HT radiator 60 by a cooling water inlet pipe 56, and the cooling water outlet in the cylinder block 3 is connected to a cooling water inlet of the HT radiator 60 by a cooling water discharge pipe 58. The cooling water inlet pipe 56 and the cooling water discharge pipe 58 are connected to each other by a bypass pipe 62 that bypasses the HT radiator 60. A thermostat 64 is provided on the cooling water inlet pipe 56 at a merging point at which the bypass pipe 62 merges with the cooling water inlet pipe 56. A mechanical water pump 66 that causes circulation of the HT cooling water is provided on the cooling water inlet pipe 56 at a point downstream of the thermostat 64. The water pump 66 is coupled to the crank shaft of the engine 1 by a belt. A temperature sensor 68 that measures the temperature of the HT cooling water having passed through the engine 1 (referred to as an HT water temperature, hereinafter) is attached to the cooling water discharge pipe 58 at a point upstream of a branch point at which the bypass pipe 62 branches from the cooling water discharge pipe 58. In this embodiment, the HT water temperature means the outlet cooling water temperature measured by the temperature sensor 68.

As described above, in the HT cooling water circulation system 50, the water pump 66 is driven by the engine 1, so that the HT cooling water is constantly circulated during operation of the engine 1. The temperature of the cooling water circulated in the HT cooling water circulation system 50 is automatically adjusted by the thermostat 64. On the other hand, in the LT cooling water circulation system 30, the electric water pump 46 is used, so that circulation of the LT cooling water can be started and stopped whether the engine 1 is running or not. In addition, the flow rate of the circulated LT cooling water can be controlled by adjusting the drive duty cycle of the electric water pump 46. In addition, the temperature of the LT cooling water circulated in the LT cooling water circulation system 30 can be actively adjusted through operation of the three way valve 44 or the electric water pump 46.

The three way valve 44 and the electric water pump 46 of the LT cooling water circulation system 30 operate under the control of a controller 100. The controller 100 adjusts the temperature of the LT cooling water flowing through the in-head LT cooling water flow channel 32 and the in-block LT cooling water flow channel 34 to an appropriate temperature by making the electric water pump 46 operate to adjust the flow rate of the LT cooling water (referred to as an LT flow rate, hereinafter) and by making the three way valve 44 operate to adjust the proportion of the LT cooling water that bypasses the LT radiator 40.

The cooling system for the engine 1 configured as described above corresponds to the disclosure set forth in the claims as follows. That is, the in-block HT cooling water flow channel 54 corresponds to a first cooling water flow channel, and the HT cooling water corresponds to a first cooling water. And, the in-block LT cooling water flow channel 34 corresponds to a second cooling water flow channel, and the LT cooling water corresponds to a second cooling water.

3. LT Flow Rate Control

The controller 100 controls the LT flow rate to cool essential parts of the cylinder head 2 and the cylinder block 3 to an appropriate temperature. FIG. 3 is a flowchart showing a flow of an LT flow rate control performed by the controller 100. The controller 100 repeatedly performs the routine shown by the flow at a predetermined control period that corresponds to the number of clocks of the ECU.

In Step S2, the controller 100 first sets a target LT water temperature, which is a target temperature of the LT cooling water flowing in the in-head LT cooling water flow channel 32 and the in-block LT cooling water flow channel 34. As the target LT water temperature, the controller 100 determines a cooling water temperature that allows prevention of an abnormal combustion, such as knocking. In a map stored in the ROM of the controller 100, the target LT water temperature is associated with the operational state of the engine 1, which is determined by the engine speed and the load (more specifically, charging efficiency).

In Step S4, the controller 100 then performs a required correction to the target LT water temperature set in Step S2. The controller 100 has an LT water temperature learning capability of learning the LT water temperature based on the result of detection of knocking. With the LT water temperature learning capability, the controller 100 reduces the LT water temperature and learns the temperature that allows prevention of knocking when a signal from the combustion pressure sensor 22 shows that knocking has been detected. The controller 100 calculates a correction to the target LT water temperature from the temperature learned with the LT water temperature learning capability, and modifies the target LT water temperature so as to reflect the correction. The controller 100 further has a capability of correcting the target LT water temperature in response to occurrence of LSPI. This capability will be described in detail later.

In Step S6, the controller 100 then calculates a required LT flow rate, which is a required value of the LT flow rate, from the target LT water temperature corrected in Step S4. Specifically, the controller 100 calculates a feed-forward term of the required LT flow rate by referring to a prepared map that associates the target LT water temperature and the required LT flow rate, and calculates a feedback term of the required LT flow rate according to a feedback control based on the difference between the target LT water temperature and a current temperature (outlet temperature) of the LT cooling water measured by the temperature sensor 48.

In Step S8, the controller 100 then determines the drive duty cycle of the electric water pump 46 from the required LT flow rate determined in Step S6. If the LT cooling water circulation system 30 is provided with a valve that adjusts the LT flow rate, the LT flow rate can also be adjusted by adjusting the opening of the valve.

In Step S10, the controller 100 finally makes the electric water pump 46 operate with the drive duty cycle determined in Step S8 to pass the cooling water through the in-head LT cooling water flow channel 32 and the in-block LT cooling water flow channel 34. As a result, the LT flow rate changes, and essential parts of the cylinder head 2 and the cylinder block 3 are cooled to an appropriate temperature.

4. Detection of LSPI

LSPI is an abnormal combustion before normal ignition by the ignition plug 20 that is caused by oil drops or the like in the combustion chamber 6 catching fire. FIG. 4 is a graph showing an LSPI occurrence region. As shown in FIG. 4, operational regions determined by the engine speed and the load (specifically, charging efficiency) include a low speed and high load region where LSPI is likely to occur. FIG. 4 also shows the ratio between PFI that is fuel injection by the port injection valve 24 and DI that is fuel injection by the in-cylinder injection valve 26 in each operational region. The ratio between PFI and DI is 50 to 50 in a low load region, while the ratio between PFI and DI is 0 to 100 in a high load region. The higher proportion of the fuel injection by the in-cylinder injection valve 26 is a cause of LSPI in the low speed and high load region.

If LSPI occurs, the pressure in the combustion chamber 6 abnormally rises. The controller 100 detects the LSPI by receiving and processing a signal from the combustion pressure sensor 22. LSPI causes deterioration of the main body and parts of the engine 1. How far the engine 1 has been deteriorated, that is, the degree of deterioration of the engine 1 depends on the history of LSPI occurrence. The history of LSPI occurrence includes the number of repetitions of LSPI, the frequency of occurrence of LSPI, the intensity of each LSPI, and the like.

The controller 100 counts, by means of a counter, the cumulative number of LSPIs since the vehicle was set to be offline. Since it is considered that the engine 1 is deteriorated each time LSPI occurs, it can be considered that the degree of deterioration becomes significant as the cumulative number increases. Therefore, the cumulative number of LSPIs counted by the controller 100 can be used as an index value of the degree of deterioration of the engine 1. Although the combustion pressure sensor 22 is used to detect LSPI in this embodiment, a knock sensor may be used as means of detecting LSPI. Whether an oscillation detected by the knock sensor is caused by knocking or LSPI can be determined from the intensity of the oscillation and the detected crank angle.

5. First LSPI Suppression Control

5-1. Summary of First LSPI Suppression Control

Even if LSPI is detected, the controller 100 does not immediately take a measure to suppress the LSPI. This is because preventing deterioration of fuel consumption and emission performance takes precedence over improving the operability by taking such a measure. However, as LSPI repeatedly occurs, deterioration of the main body and parts of the engine 1 progresses and can cause damage to parts or other defects that can hinder the vehicle from running. To avoid such a trouble, the controller 100 performs a process of suppressing LSPI on a condition that the cumulative number of LSPIs is greater than a threshold that depends on the mileage of the vehicle.

The controller 100 can suppress LSPI in two processes. A first process is to lower the proportion of the fuel injection by the in-cylinder injection valve 26 to raise the proportion of the fuel injection by the port injection valve 24. If the proportion of the fuel injection by the in-cylinder injection valve 26 is lowered, dilution of the oil on the wall of the cylinder 4 with the fuel that can leads to occurrence of LSPI is suppressed, so that the frequency of occurrence of LSPI and therefore the progression of the deterioration are suppressed.

The controller 100 sets the following three conditions for performing the first process. A first condition for the first process is that the cumulative number of LSPIs is greater than a first threshold. The first threshold is a function of the mileage. The first threshold becomes greater as the mileage increases. How far the engine 1 has been deteriorated depends on the cumulative number of LSPIs with respect to the mileage, that is, the frequency of occurrence of LSPI. Therefore, the first threshold is determined from the frequency of occurrence of LSPI that is allowed to attain the mileage to be secured.

A second condition for the first process is that the engine 1 runs in the LSPI occurrence region. In a control program of the controller 100, the LSPI occurrence region is previously determined by the engine speed and the load. When the engine 1 runs in the previously determined operational region (determined operational region), the LSPI is more likely to occur than when the engine 1 runs in the other operational regions. In other words, when the engine 1 is running in the other operational regions than the determined operational region, the probability of occurrence of LSPI is low, so that the first process does not need to be performed or, on the contrary, is preferably not performed from the viewpoint of fuel consumption and emission performance.

A third condition for the first process is that the LT water temperature is lower than a predetermined threshold temperature. In the map in which the target LT water temperature is set, the target LT water temperature is initially set at a temperature at which LSPI is unlikely to occur. If the LT water temperature learning capability works, however, the LT water temperature can be reduced to be lower than the initially set value in order to suppress knocking. If a cooling abnormality occurs in the HT cooling water circulation system 50 and the HT water temperature does not fall, the drive duty cycle of the electric water pump 46 can be maximized to compensate for the loss of cooling by the HT cooling water circulation system 50 with cooling by the LT cooling water. In such a case, the LT water temperature can excessively fall, and the temperature of the intake port 10 cooled by the in-head LT cooling water flow channel 32 or the part of the peripheral wall of the cylinder 4 close to the combustion chamber 6 that is cooled by the in-block LT cooling water flow channel 34 can excessively fall. In that case, evaporation of the fuel injected from the in-cylinder injection valve 26 slows down, and dilution of the oil on the wall surface of the cylinder 4 with the fuel progresses. A threshold temperature that serves as a criterion of the determination of whether the third condition is satisfied or not is set at a temperature at which occurrence of LSPI becomes marked (from 40° C. to 50° C., for example).

The controller 100 performs the first process only when all of the three conditions described above are satisfied. In the first process, the proportion of the fuel injection by the in-cylinder injection valve 26 is lowered to raise the proportion of the fuel injection by the port injection valve 24 compared with before the index value exceeds the first threshold. More specifically, the ratio between PFI and DI is changed from 0 to 100 to 50 to 50.

An engine control that involves performing the first process based on the determination of whether the three conditions described above are satisfied or not is referred to as a “first LSPI suppression control”. A control program for the first LSPI suppression control is stored in the ROM of the controller 100.

5-2. Flow of First LSPI Suppression Control

FIG. 5 is a flowchart showing a flow of the first LSPI suppression control performed by the controller 100. The controller 100 repeatedly performs the routine shown by the flow at a predetermined control period that corresponds to the number of clocks of the ECU.

In Step S102, the controller 100 first reads the LT water temperature (ethwl) measured by the temperature sensor 48. In Step S104, the controller 100 then compares the LT water temperature (ethwl) read in Step S102 with a threshold temperature (THt) to determine whether or not the LT water temperature is lower than the threshold temperature. The determination in Step S104 is a determination concerning the third condition described above.

If the LT water temperature is lower than the threshold temperature, in Step S106, the controller 100 reads the cumulative number of LSPIs (Clspi). As described above, the cumulative number of LSPIs counted by the counter is incremented each time LSPI is detected. In Step S108, the controller 100 then compares the cumulative number (Clspi) read in Step S106 with a first threshold (THc1) to determine whether or not the cumulative number of LSPIs is greater than the first threshold. The first threshold is associated with the mileage in the map, and the value of the first threshold associated with the current mileage is read from the map. The determination in Step S108 is a determination concerning the first condition described above.

If the cumulative number of LSPIs is greater than the first threshold, in Step S110, the controller 100 reads the engine speed (NE) and the load (KL). The load (charging efficiency) is calculated from the intake air amount measured by an air flowmeter and the engine speed. In Step S112, the controller 100 then determines whether or not the operating point of the engine 1, which is determined by the engine speed and the load read in Step S110, lies in the determined operational region, which corresponds to the LSPI occurrence region. The determination in Step S112 is a determination concerning the second condition described above.

If the operating point of the engine 1 lies in the determined operational region and all of the three conditions described above are satisfied, in Step S114, the controller 100 changes the injection ratio between the in-cylinder injection valve 26 and the port injection valve 24. That is, the controller 100 performs the first process described above. More specifically, as shown in FIG. 4 described above, the ratio between PFI and DI in the high load region, which is initially set to be 0 to 100, is changed to 50 to 50, which is the same as the ratio between PFI and DI in the low load region.

If the result of any one of the determinations in Steps S104, S108 and S112 is negative, the processing in Step S114 is not performed. In that case, a preset injection ratio is maintained.

5-3. Effect of First LSPI Suppression Control

FIG. 6 shows a graph showing how the cumulative number of LSPIs changes with the mileage. The curve shown by a thin solid line shows how the cumulative number of LSPIs changes with the mileage in a typical engine provided with one cooling system. The curves shown by a dashed line and a thick solid line show how the cumulative number of LSPIs changes with the mileage in the engine provided with two, low-temperature and high-temperature, cooling systems. In the engine provided with two cooling systems, such as the engine according to this embodiment, the LT water temperature learning capability works to suppress knocking, and therefore, LSPI can become more likely to occur in the low speed and high load region, and the cumulative number of LSPIs increases with the mileage at a higher rate than in the engine provided with one cooling system. FIG. 6 shows an example of such a situation.

The difference between the cases shown by the curve shown by the dashed line and the curve shown by the thick solid line is whether the first LSPI suppression control is performed or not. If the first LSPI suppression control is not performed, as shown by the dashed line, the cumulative number of LSPIs increases at a high rate, and a fail-safe operation can be required early. In the fail-safe operation, the highest priority is assigned to preventing damage due to the deterioration of the engine 1, and therefore, measures having a great influence on the operability or other performance of the engine 1, such as torque limitation, are taken.

To the contrary, if the first LSPI suppression control is performed, as shown by the thick solid line, the cumulative number of LSPIs increases at a reduced rate once the cumulative number of LSPIs exceeds a first threshold line (a line that shows how the first threshold changes with the mileage). If the cumulative number of LSPIs becomes lower than the first threshold line, the first process is no longer performed, so that the cumulative number of LSPIs increases at a higher rate again. Since the first process is performed each time the cumulative number exceeds the first threshold line, the cumulative number of LSPIs generally changes along the first threshold line. As a result, progression of the deterioration of the engine 1 can be slowed down, and the engine 1 can remain useful until the intended mileage is attained.

6. Second LSPI Suppression Control

6-1. Summary of Second LSPI Suppression Control

A second process performed by the controller 100 to suppress LSPI is a process of increasing the LT water temperature. If the LT water temperature is increased and brought close to the HT water temperature, the temperature of the wall of the cylinder 4 cooled by the LT cooling water (the part of the wall of the cylinder 4 that is close to the combustion chamber 6) increases to facilitate evaporation of the fuel injected from the in-cylinder injection valve 26, so that dilution of the oil on the wall of the cylinder 4 with the fuel that leads to occurrence of LSPI is suppressed. However, if the LT water temperature is increased, the advantage of the engine 1 having the two, low-temperature and high-temperature, cooling systems decreases.

The controller 100 sets the following two conditions for performing the second process. A first condition for the second process is that the cumulative number of LSPIs is greater than a second threshold, which is greater than the first threshold. As with the first threshold, the second threshold is a function of the mileage. Since the second threshold is greater than the first threshold, when the first process of the first LSPI suppression control is performed, and the rate of increase of the cumulative number of LSPIs is reduced, the cumulative number of LSPIs is unlikely to be greater than the second threshold. That is, the second process is a secondary fail-safe process that is performed only when the rate of increase of the cumulative number of LSPIs is not reduced even if the first process is performed.

A second condition for the second process is that the engine 1 runs in the LSPI occurrence region. The second process is performed only when the engine 1 is running in the determined operational region, which corresponds to the LSPI occurrence region.

The controller 100 performs the second process only when both the two conditions described above are satisfied. In the second process, compared with before the index value exceeds the second threshold, the LT water temperature is increased, or more specifically, the target LT water temperature is corrected to a higher temperature. The corrected target LT water temperature is set to be a higher value as the difference between the cumulative number of LSPIs and the second threshold increases.

An engine control that involves performing the second process based on the determination of whether the two conditions described above are satisfied or not is referred to as a second LSPI suppression control. A control program for the second LSPI suppression control is stored in the ROM of the controller 100.

6-2. Flow of Second LSPI Suppression Control

FIG. 7 is a flowchart showing a flow of the second LSPI suppression control performed by the controller 100. The controller 100 repeatedly performs the routine shown by the flow at a predetermined control period that corresponds to the number of clocks of the ECU. The controller 100 performs the routine of the second LSPI suppression control in parallel with the routine of the first LSPI suppression control.

In Step S202, the controller 100 first reads the cumulative number of LSPIs (Clspi). In Step S204, the controller 100 then compares the cumulative number (Clspi) read in Step S202 with a second threshold (THc2) to determine whether or not the cumulative number of LSPIs is greater than the second threshold. The second threshold is associated with the mileage in the map, and the value of the second threshold associated with the current mileage is read from the map. The determination in Step S204 is a determination concerning the first condition described above.

If the cumulative number of LSPIs is greater than the second threshold, in Step S206, the controller 100 reads the engine speed (NE) and the load (KL). In Step S208, the controller 100 then determines whether or not the operating point of the engine 1, which is determined by the engine speed and the load read in Step S206, lies in the determined operational region, which corresponds to the LSPI occurrence region. The determination in Step S208 is a determination concerning the second condition described above.

If the operating point of the engine 1 lies in the determined operational region, and both the two conditions described above are satisfied, in Step S210, the controller 100 calculates a correction value for the target LT water temperature. That is, the controller 100 performs the second process described above. A map in which the correction value is associated with the difference between the cumulative number of LSPIs (Clspi) and the second threshold (THc2) is stored in the ROM of the controller 100. FIG. 7 shows an example of the map. In this example, the correction value is 2° C. when the cumulative number of LSPIs is equal to the second threshold, and increases in increments of 2° C. each time the cumulative number of LSPIs increases by one. In Step S4 of the LT flow rate control described above, the correction value calculated in Step S210 is added to the target LT water temperature set in Step S2 of the LT flow rate control.

If the result of any one of the determinations in Steps S204 and S208 is negative, the processing in Step S210 is not performed. In that case, the current LT water temperature is maintained.

6-3. Effect of Second LSPI Suppression Control

FIG. 8 shows a graph showing how the cumulative number of LSPIs changes with the mileage in the engine according to this embodiment. In the example shown in this graph, when the cumulative number of LSPIs exceeds the first threshold line, the first process is performed, and the rate of increase of the cumulative number of LSPIs is temporarily reduced. However, the rate of increase of the cumulative number of LSPIs then increases again.

If only the first LSPI suppression control is performed, the cumulative number of LSPIs continues increasing at a high rate, and the fail-safe operation can be eventually required. According to this embodiment, however, not only the first LSPI suppression control but also the second LSPI suppression control is performed, so that the cumulative number of LSPIs increases at a reduced rate once the cumulative number of LSPIs exceeds a second threshold line (a line that shows how the second threshold changes with the mileage). As a result, progression of the deterioration of the engine 1 can be slowed down, and the engine 1 can remain useful until the intended mileage is attained.

7. Others

In the embodiment described above, LSPIs are detected, and the cumulative number of LSPIs is used as an index value of the degree of deterioration of the engine 1. Alternatively, a parameter weighted by the intensity of LSPI may be calculated each time LSPI occurs, and a cumulative value of the parameters may be used as an index value. The intensity of LSPI can be estimated from the amplitude of the combustion pressure measured by the combustion pressure sensor 22, for example. Alternatively, a parameter weighted by the frequency of occurrence of LSPI may be calculated each time LSPI occurs, and a cumulative value of the parameters may be used as an index value. The frequency of occurrence of LSPI is defined as the number of times of occurrence of LSPI for a certain mileage or running time. The frequency of occurrence of LSPI may be simply an inverse of the mileage or running time between the previous occurrence of LSPI and the current occurrence of LSPI.

Although the mileage is used as a parameter that determines the first threshold and the second threshold in the embodiment described above, the running time of the engine 1 may be used as a parameter to determine the first threshold and the second threshold. In particular, the running time of the engine 1 in the LSPI occurrence region (determined operational region) is preferably used as a parameter to determine the first threshold and the second threshold.

The second LSPI suppression control is not always essential. If at least the first LSPI suppression control is performed, progression of the deterioration of the engine 1 can be slowed down, and the engine 1 can remain useful until the intended mileage is attained. The second LSPI suppression control is a control that is preferably performed to further ensure that the engine 1 remains useful until the intended mileage is attained. 

What is claimed is:
 1. A controller for an internal combustion engine, the internal combustion engine comprising: an in-cylinder injection valve that directly injects fuel into a combustion chamber formed in an upper part of a cylinder; a port injection valve that injects the fuel into an intake port; a first cooling water flow channel used to cool a part of a peripheral wall of the cylinder; and a second cooling water flow channel used to cool, with second cooling water, the intake port or a part of the peripheral wall of the cylinder that is closer to the combustion chamber than the part cooled by the first cooling water flow channel, the second cooling water flowing in the second cooling water flow channel being at a lower temperature than first cooling water flowing in the first cooling water flow channel, wherein the controller is configured to calculate an index value of a degree of deterioration of the internal combustion engine caused by LSPI; and to reduce a proportion of fuel injection by the in-cylinder injection valve to increase a proportion of fuel injection by the port injection valve compared with before the index value exceeds the first threshold, wherein if the index value exceeds a first threshold, when the temperature of the second cooling water is lower than a threshold temperature, and the internal combustion engine is running in a determined operational region set in a low speed and high load region.
 2. The controller for an internal combustion engine according to claim 1, further configured, wherein if the index value exceeds a second threshold that is greater than the first threshold, when the internal combustion engine is running in the determined operational region, to increase the temperature of the second cooling water compared with before the index value exceeds the second threshold. 